[worn]

Ball bearings or small nuts & bolts inside & shaking around helps too.. if you do a search this has been covered plenty of times on the board.

I've used dry wall screws and paid my son (he was 10 at the time) to shake it as long as he could for a few days, then flushed it out and it looked almost like new just from the screws rattling around. Add some vinegar to the screws, seal and shake, then flush and reseal.